A ferrule for an optical connector is an important element of the optical connector used in optical communication to position and fix an optical fiber.
A typical resinous ferrule has a cross section as shown in FIGS. 1A or 1B. The ferrule 3 of FIG. 1A is wholly made of a resin while a part of the outer periphery of that of FIG. 1B is surrounded by a metal tube 4. In these figures, numerals 1 and 2 stand for a coated optical fiber and an optical fiber, respectively.
The conventional resinous ferrule is made by molding an epoxy resin containing glass fiber or silica. For example, Japanese Patent Kokai Publication (unexamined) No. 97014/1983 discloses a ferrule for an optical connector made of an epoxy resin containing minute balls of quartz glass in an amount of 30 to 80% by weight. Japanese Patent Kokai Publication (unexamined) No. 176012/1982 discloses molding of a ferrule from a resin containing glass fiber.
Further, Report No. 2234 (1984) in the National Meeting of the Denki Gakkai (Electric Society) (entitled "Reliability of Single Core Connector for Direct Connection of Coated Optical Fiber") describes the use of an epoxy resin for enclosing LSI, in which silica is used as a filler.
However, the conventional resinous ferrules for the optical connector have several drawbacks.
The first drawback is their poor reliability. When, as shown in FIG. 3, the flange portion is fixed in a bed and flexural load F is applied at the upper end of the ferrule 3 at a rate of 50 mm/min., the ferrule is broken at the load of 3.3 kg in average. This fracture strength is less than a fourth of that of a metal ferrule for an optical connector. Therefore, the resinous ferrule has poor reliability such that it is broken when extraordinary force is applied on it during attaching or detaching the optical connector.
The second drawback is inferior accuracy of an outer diameter of the ferrule during molding of the resinous ferrule. An accuracy of the outer diameter of the ferrule should be very strict and is required to be in a range of .+-.0.001 mm. However, the molding of the resin is inevitably accompanied with thermal expansion or shrinkage when cured. This is expressed by a mold shrinkage factor. For example, when an article having a diameter of 2.499.+-.0.001 mm is molded from a resin having a mold shrinkage factor of 0.5%, an inner diameter of a mold should be 2.512 mm. If the mold shrinkage factor varies by 10%, the outer diameter of the molded article does not fall within 2.499.+-.0.001 mm. Since the mold shrinkage factor is related to various factors such as molding conditions and a kind of the resin to be molded, it is difficult to precisely control the mold shrinkage factor. Thus, it is highly desired to offer a resin having a small mold shrinkage factor so that its variation does not affect the accuracy of the dimensions of the article.